Difference between revisions of "DSP Group Truespeech"

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(skeleton description)
 
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* Format tag: 0x22
 
* Format tag: 0x22
 
* Company: [[DSP Group]]
 
* Company: [[DSP Group]]
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This is the codec developed by [[DSP Group]]. It operates on 8000 Hz, 16-bit mono [[PCM]] and have some fixed bitrates, Windows version supports 15:1 compression (~1 Kbps) only.
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== Technical details (for standard scheme) ==
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This codec employs LPC (Linear Predictive Coding) as almost every speech codec does.
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Frame (240 samples) is divided into 4 subframes.
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Packed frame data holds 8-order filter used in synthesis, 4x7 pulse positions and values, offset in previously decoded frame.
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Decoding flow:
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  unpack frame data
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  reconstruct packed filter
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  merge this filter with previous to create 4 filters for each subframe
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  for each subframe {
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    apply twopoint filter on some saved data
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    place pulses (7 pulses for each subframe max)
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    update saved filter
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    apply main filter to subframe data (mostly pulses)
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  }
  
 
[[Category: Audio Codecs]]
 
[[Category: Audio Codecs]]

Revision as of 22:55, 8 February 2006

This is the codec developed by DSP Group. It operates on 8000 Hz, 16-bit mono PCM and have some fixed bitrates, Windows version supports 15:1 compression (~1 Kbps) only.

Technical details (for standard scheme)

This codec employs LPC (Linear Predictive Coding) as almost every speech codec does.

Frame (240 samples) is divided into 4 subframes.

Packed frame data holds 8-order filter used in synthesis, 4x7 pulse positions and values, offset in previously decoded frame.

Decoding flow:

 unpack frame data
 reconstruct packed filter
 merge this filter with previous to create 4 filters for each subframe
 for each subframe {
   apply twopoint filter on some saved data
   place pulses (7 pulses for each subframe max)
   update saved filter
   apply main filter to subframe data (mostly pulses)
 }